Interpretive Summary: Traditional calf-rearing programs limit nutrient intake from milk replacer during the first few weeks of life to promote dry-feed intake and early weaning. Dramatic improvements in growth rate and feed efficiency resulting from feeding greater amounts of milk replacer with higher protein concentrations have led to the development of intensified feeding programs. Improving the plane of nutrition also may benefit the immune system of the calf, decreasing morbidity and mortality associated with infectious diseases. Effects of growth rate on immune function in vaccinated, milk replacer-fed calves are not well characterized. Results from this study demonstrate that calves fed to achieve no-, low-, and high-growth rates mount similar immune responses after vaccination. Results also suggest that limiting growth, in the absence of weight loss, is not detrimental to specific aspects of immune function and that a high rate of growth during neonatal period does not enhance immune responses of the calf. This work will provide researchers, producers, and veterinarians new information regarding nutrition and immune function in the calf.

Technical Abstract:
Effects of growth rate on immune function in preruminant calves are not well characterized. This study shows that calves fed the same milk replacer to achieve three growth rates (no, low, and high growth) mount similar immune responses to vaccination. Immune cells from high-growth calves, however, were less viable when compared with the cell populations from low- and no-growth calves. Results suggest that malnutrition in the absence of weight loss is not detrimental to immune responses and that a high growth rate does not enhance these responses. Effects of growth rate on infectious disease susceptibility need to be investigated further.